How do you pass arguments with UnityEvents?

Question

I was inspired by a great talk at Unite by Ryan Hipple.

His examples didn’t cover passing arguments with UnityEvents

Do I need to extend UnityEvent, GameEvent and GameEventListener from a generic base class for this to work properly?

If so do I need to make a new set of classes for each Type and combination of Types that I want to pass?

Game Event Scriptable Object

[CreateAssetMenu]
    public class GameEvent : ScriptableObject
    {
        /// <summary>
        /// The list of listeners that this event will notify if it is raised.
        /// </summary>
        private readonly List<GameEventListener> eventListeners = 
            new List<GameEventListener>();

        public void Raise()
        {
            for(int i = eventListeners.Count -1; i >= 0; i--)
                eventListeners[i].OnEventRaised();
        }

        public void RegisterListener(GameEventListener listener)
        {
            if (!eventListeners.Contains(listener))
                eventListeners.Add(listener);
        }

        public void UnregisterListener(GameEventListener listener)
        {
            if (eventListeners.Contains(listener))
                eventListeners.Remove(listener);
        }
    }

Listener Class

public class GameEventListener : MonoBehaviour
    {
        [Tooltip("Event to register with.")]
        public GameEvent Event;

        [Tooltip("Response to invoke when Event is raised.")]
        public UnityEvent Response;

        private void OnEnable()
        {
            Event.RegisterListener(this);
        }

        private void OnDisable()
        {
            Event.UnregisterListener(this);
        }

        public void OnEventRaised()
        {
            Response.Invoke();
        }
    }

Hellium · Accepted Answer · 2018-04-19 07:35:21Z

3

Yes, you will have to create a sub-class of the UnityEvent class as follow:

[System.Serializable]
public class GameObjectEvent : UnityEngine.Events.UnityEvent<GameObject> {} // Leave it empty

And then:

public class GameEventListener : MonoBehaviour
{
    [Tooltip("Event to register with.")]
    public GameEvent Event;

    [Tooltip("Response to invoke when Event is raised.")]
    public GameObjectEvent Response;

    private void OnEnable()
    {
        Event.RegisterListener(this);
    }

    private void OnDisable()
    {
        Event.UnregisterListener(this);
    }

    public void OnEventRaised()
    {
        Response.Invoke( gameObject );
    }
}

I have never found an alternative to create a new class for every type, except using System.Action<your_type>, but you won't be able to use the Inspector anymore to call the function you want (unless you have a plugin to serialize the System.Action)

answered Apr 19, 2018 at 7:35

Hellium

2,9491 gold badge13 silver badges27 bronze badges

\$\begingroup\$ Can you pass in custom classes or only game objects and primitives ? \$\endgroup\$

Pyreal
– Pyreal

2018-04-19 21:18:23 +00:00
Commented Apr 19, 2018 at 21:18
\$\begingroup\$ You can pass the type you want :) \$\endgroup\$

Hellium
– Hellium

2018-04-20 07:00:01 +00:00
Commented Apr 20, 2018 at 7:00
1

\$\begingroup\$ Fortunately you no longer need to create your own custom type. As of 2020, the Unity serializer now handles this type of generic natively, so UnityEvent<GameObject> is all you need. \$\endgroup\$

DMGregory
– DMGregory ♦

2022-03-15 02:11:49 +00:00
Commented Mar 15, 2022 at 2:11

Add a comment |

Karolis Vaitkevicius · Accepted Answer · 2022-03-15 00:03:49Z

(Can't comment but this is expanding on what Hellium said)
Worth noting that you will need to adjust the Raised and OnEventRaised methods accordingly as well:

public void OnEventRaised(GameObject gameObject)
{
    Response.Invoke( gameObject );
}

Like this in the inspector it will show up to select a dynamic gameObject, which is the one that will be passed on from wherever you're going to be invoking the event:

EventName?.Invoke(gameObject);

For me this was useful for this case:
DamageTakenEvent?.Invoke(collision.gameObject);

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